Physconia subpallida (Common Name: Pale-bellied Frost Lichen) is a conspicuous macrolichen endemic to eastern North America that is currently listed as endangered in Canada and should be listed in the United States. Major declines have been documented across its range in the last several decades. The species is now extremely rare and appears to have been extirpated from most of its range. It continues to be threatened by multiple forces.
Physconia subpallida is endemic to the Appalachian-Great Lakes and Ozarks regions of eastern North America.
Demographic studies are needed to assess and monitor the sizes of remaining populations. Study of an extant population in Ontario has shown it to be stable since 2004, however the vast majority of populations are known only from historical occurrences. Studies of herbarium vouchers have shown that the size of individuals, and frequency of fruiting bodies, has decreased over time. We classify the population trends as deteriorating.
This species occurs primarily on the bark of hardwood trees in temperate hardwood forests, especially mature stands. It has also rarely been found on wood and limestone and seems to require substrates with high pH and moisture holding capacity.
The widespread decline experienced by this species was likely due to a combination of the large scale loss/degradation of habitats throughout its range as well as air pollution following the industrial revolution. The current threats to this species stem primarily from 1) changes in habitat (macro- and micro- scales) resulting from deposition of pollutants and ecosystem alterations, 2) changes in habitat (macro- and micro- scales) that are likely to result from climate change and 3) changes in habitat (macro- and micro- scales) resulting conversion and deterioration of natural habitats both historically and ongoing.
There are many conservation actions that can be taken including educating and training land managers and local botanists to identify the species so we can monitor its health, federally listing the species as endangered in the United States, improving air quality regulation, and providing increased protection for forest stands where the species occurs and could occur in the future.
The distribution of this species is well understood. Further research that will aid in the conservation of this species includes population assessments and monitoring, population genetics studies, and ecological studies that incorporate threats to the species. Additionally, a species recovery plan needs to be written for the United States.
Executive Summary: Ontario
http://www.registrelep-sararegistry.gc.ca/virtual_sara/files/cosewic/sr_Pale-bellied frost lichen_0810_e.pdf
Esslinger, TL 1994: New species and new combinations in the lichen genus Physconia in North America. - Mycotaxon 51: 91-99.
Nelsen, M. P. 2005: Additions to the lichen flora of Wisconsin with new records of rare species. - Michigan Botanist 44(4): 188-191.